U.S. patent number 8,315,188 [Application Number 12/749,622] was granted by the patent office on 2012-11-20 for topology database synchronization.
This patent grant is currently assigned to Brocade Communications System, Inc.. Invention is credited to Vineet Abraham, Ezio Valdevit.
United States Patent |
8,315,188 |
Valdevit , et al. |
November 20, 2012 |
Topology database synchronization
Abstract
A network comprises a plurality of interconnected switches that
implement a topology database synchronization technique in which
each switch determines whether its topology database has already
been transmitted to a neighboring switch when a new link is formed
to the neighboring switch. When a new electrical connection is
detected, the local switch determines whether any of its other
ports have already been connected to the same neighboring switch.
If no other port on the local switch has been connected to the
neighboring switch, the local switch transmits its topology
database to the neighboring switch. If the local switch determines
that it has already been connected to the neighboring switch via
another one of its ports, the local switch does not yet again copy
of the database to the neighboring switch. Also, link state record
updates are propagated via only one inter-switch link to a
neighboring switch, not all possible links.
Inventors: |
Valdevit; Ezio (Redwood City,
CA), Abraham; Vineet (San Jose, CA) |
Assignee: |
Brocade Communications System,
Inc. (San Jose, CA)
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Family
ID: |
31187195 |
Appl.
No.: |
12/749,622 |
Filed: |
March 30, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100182936 A1 |
Jul 22, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10210019 |
Jul 31, 2002 |
7769902 |
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Current U.S.
Class: |
370/254; 370/387;
709/248; 370/328; 370/400 |
Current CPC
Class: |
H04L
41/12 (20130101) |
Current International
Class: |
H04L
12/28 (20060101); G06F 15/16 (20060101) |
Field of
Search: |
;370/254,386,387,400
;709/248 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kizou; Hassan
Assistant Examiner: Maglo; Emmanuel
Attorney, Agent or Firm: Conley Rose, P.C.
Claims
What is claimed is:
1. A method, comprising: (a) detecting a connection to a port on a
switch, wherein the connection stems from a first switch; (b)
determining whether another port on the switch has already been
connected to the first switch; and (c) if no other port on the
switch is already connected to the first switch, transmitting the
switch's topology database to the first switch; or (d) if another
port on the switch is already connected to the first switch over
which the switch's topology database was previously transmitted,
not transmitting the switch's topology database to the first switch
over the connection detected in (a).
2. The method of claim 1 wherein (c) and (d) comprise transmitting
data to the first switch indicating an end of a topology database
exchange sequence.
3. The method of claim 1 wherein (b) comprises determining whether
another port on the switch is in a state permitting the another
port to be used to transmit traffic.
4. The method of claim 1 further comprising before performing (b),
transmitting connectivity information to said first switch.
5. The method of claim 1 further comprising updating a link state
record for each new inter-switch link and transmitting said updated
link state record to a second switch via only one of a plurality of
ports of the switch connected to said second switch.
6. The method of claim 5 further comprising selecting one of said
plurality of ports of the switch connected to said second switch to
be a master port and transmitting said updated link state record
via said master port to said second switch.
7. The method of claim 6 further comprising selecting another of
said plurality of switch ports connected to said second switch to
be a replacement master if said master port becomes unusable to
transmit traffic.
8. The method of claim 7 wherein each of the plurality of ports
connected to said second switch is assigned a unique number and
selecting another of said plurality of switch ports connected to
said second switch to be the replacement master comprises
selecting, among the remaining of said plurality of ports connected
to said second switch, a port having the lowest port number.
9. The method of claim 7 wherein each of the plurality of ports
connected to said second switch is assigned a unique number and
selecting another of said plurality of local switch ports connected
to said second switch to be the replacement master includes
selecting, among the remaining of said plurality of ports connected
to said second switch, a port having the highest port number.
10. A method, comprising (a) among a plurality of ports on a single
switch, the plurality of ports connecting the single switch to a
single first switch, selecting one of said ports to be a master
port; (b) updating a link state record containing connectivity
information regarding a newly established inter-link switch between
said single switch and a neighboring switch; and (c) transmitting
said updated link state record over said master port.
11. The method of claim 10 further comprising: (d) selecting a
replacement master port if said master port ceases to be usable to
transmit traffic.
12. The method of claim 11 wherein each port on said single switch
is assigned a unique number and (d) comprises selecting the port,
out of the plurality of ports connecting the single switch to the
single first switch, having the lowest number as the replacement
master port.
13. The method of claim 11 wherein each port on said single switch
is assigned a unique number and (d) comprises selecting the port,
out of the plurality of ports connecting the single switch to the
single first switch, having the highest number as the replacement
master port.
14. A device, comprising: a CPU; a plurality of ports; memory
coupled to said CPU and comprising a topology database; wherein,
when said CPU is adapted to detect over one of its plurality of
ports a first neighboring switch, said CPU: is adapted to determine
whether another port out of the plurality of ports is already
connected to said first neighboring switch; and if the device does
not include the another port already connected to said first
neighboring switch, said CPU is adapted to transmit the topology
database to said first neighboring switch; or if the device does
include the another port already connected to said first
neighboring switch, said CPU does not transmit the topology
database to said first neighboring switch.
15. The device of claim 14 wherein, regardless of whether the
device includes the another port already connected to said first
neighboring switch, said CPU is adapted to transmit data to the
first neighboring switch indicating an end of a topology database
exchange sequence.
16. The device of claim 14 wherein said device is configured to
connect to a second neighboring switch via a first plurality of
ports and wherein said CPU is adapted to update a link state record
for each new link established to said first neighboring switch and
transmit said updated link state record to the second neighboring
switch via only one of said first plurality of ports.
17. The device of claim 15 wherein determining whether the another
port is already connected to said first neighboring switch
comprises determining whether the another port on the device is in
a state permitting the another port to be used to transmit
traffic.
18. The device of claim 16 wherein said CPU is adapted to select
one of said first plurality of ports to be a master port and
transmit said updated link state record via said master port.
19. The device of claim 18 wherein said CPU is adapted to select
another of said first plurality of ports to be a replacement master
port if said master port becomes unusable to transmit traffic.
20. The device of claim 19 wherein said CPU assigns a unique number
to each of said plurality of ports and selects the replacement
master port by selecting another of said first plurality of ports
having the lowest port number.
21. The device of claim 19 wherein said CPU assigns a unique number
to each of said plurality of ports and selects the replacement
master port by selecting another of said first plurality of ports
having the highest port number.
22. A device, comprising: a plurality of ports usable to connect to
a second neighboring switch; memory comprising link state records;
a CPU coupled to said memory, said CPU is adapted to: update a link
state record containing connectivity information regarding
connections between the device and a first neighboring switch; and
transmit said updated link state record to the second neighboring
switch via only one port out of the plurality of ports connected to
the second neighboring switch only if said updated link state
record was not previously transmitted to the second neighboring
switch through any of the plurality of ports.
23. The device of claim 22 wherein said CPU selects one of said
plurality of ports to be a master port through which CPU transmits
said updated link state record.
24. The device of claim 23 wherein said CPU selects a replacement
master port out of the plurality of ports connected to the second
neighboring switch if said previously selected master port ceases
to be usable to transmit network traffic.
25. The device of claim 24 wherein each port on said device is
assigned a unique number and said CPU selects the port, out of the
plurality of ports connected to the second neighboring switch,
having the lowest number as the replacement master port.
26. The device of claim 24 wherein each port on said network device
is assigned a unique number and said CPU selects the port, out of
the plurality of ports connected to the second neighboring switch,
having the lowest number as the replacement master port.
27. A non-transitory machine-readable storage medium comprising
instructions that, when executed by a processor, cause the
processor to: (a) detect an electrical connection between a port on
a switch and a first switch; (b) determine whether another port on
the switch has already been connected to the first switch; and (c)
if no other port on the switch is already connected to the first
switch, transmit the switch's topology database to the first
switch; or (d) if another port on the switch is already connected
to the first switch over which the switch's topology database was
previously transmitted, not transmit the switch's topology database
to the first switch over the connection detected in (a).
28. The non-transitory machine-readable storage medium of claim 27
wherein (c) and (d) comprises transmitting data to the first switch
indicating an end of a topology database exchange sequence.
29. The non-transitory machine-readable storage medium of claim 27
wherein (b) comprises determining whether another port on the
switch is in a state permitting the another port to be used to
transmit traffic.
30. The non-transitory machine-readable storage medium of claim 27
further comprising updating a link state record for each new
inter-switch link and transmitting said updated link state record
to a second switch via only one of a plurality of local switch
ports connected to said second switch.
31. A non-transitory machine-readable storage medium comprising
instructions that, when executed by a processor, cause the
processor to: (a) among a plurality of ports connecting a single
switch to a single first switch, select one of said plurality of
ports to be a master port; (b) update a link state record
containing connectivity information regarding a newly established
inter-switch link between said single switch and a neighboring
switch; and (c) transmit said updated link state record over said
master port.
32. The non-transitory machine-readable storage medium of claim 31
further causing the processor to select a replacement master port
if said master port ceases to be usable to transmit traffic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to computer networks. More
particularly, the invention relates to electronic switches through
which communications pass from one point in a network to another.
Still more particularly, the invention relates to an improved
technique for synchronizing topology databases between switches in
a network.
2. Background Information
Initially, computers were most typically used in a standalone
manner. It is now commonplace for computers and other types of
computer-related and electronic devices to communicate with each
other over a network. The ability for computers to communicate with
one another has lead to the creation of networks ranging from small
networks comprising two or three computers to vast networks
comprising hundreds or even thousands of computers. Networks can be
set up to provide a wide assortment of capabilities. For example,
networks of computers may permit each computer to share a
centralized mass storage device or printer. Further, networks
enable electronic mail and numerous other types of services.
Generally, a network's infrastructure generally comprises switches,
routers, hubs and the like to coordinate the effective and
efficient transfer of data and commands from one point on the
network to another.
Networks often comprise a "fabric" of interconnected switches which
are devices that route data packets from a source port to a
destination port. FIG. 1 shows an exemplary switch fabric
comprising switches 20, 22, 24, 26 and 28. Various devices
including servers, storage devices, etc. connect to some or all of
the switches. In FIG. 1, devices D1 and D2 connect to switch 20 and
device D3 connects to switch 24. Through the fabric of switches,
devices D1-D3 can communicate with each other by sending and
receiving data frames. The switch fabric takes care of routing the
data frames from the source to their intended destination.
The switches shown in FIG. 1 are interconnected by communication
links typically referred to as inter-switch links ("ISLs"). As
shown, switches 22 and 24 are connected by a single ISL 17, as are
switches 24 and 26, switches 26 and 28, and switches 20 and 28.
Switch 20 connects to switch 22 by four ISLs (identified
collectively by numeral 19), as also is the case with switches 20
and 26. Multiple ISLs between a pair of switches increases the
effective bandwidth between the switches and provides redundancy in
the case of a link failure.
Each switch generates and maintains a link state record ("LSR").
The LSRs for switches 20-28 are shown as LSRs 21-29, respectively
in FIG. 1. The LSRs are stored in memory 15 which is coupled to and
accessible by a CPU 13 in each switch. Each LSR for a switch
specifies how that switch is connected to its neighboring switches.
Two switches connected directly via an ISL are referred to as
"neighbors." For example, the neighbors of switch 20 are switches
22, 26 and 28, but not switch 24 because switch 24 does not connect
via an ISL directly to switch 20. Switch 20 can communicate with
switch 24 via either switch 22 or switch 26.
Each switch includes multiple ports and the ISLs are formed between
ports of neighboring switches. Not all of a switch's ports need be
used at any point in time. The switches in FIG. 1 may be, for
example, 16 port switches. Switch 20 is shown as having nine ports
(numbered 1-9) connected via ISLs to neighboring switches 22, 26
and 28, while switches 22 and 26 only use five and six,
respectively, of their ports to connect to their neighbors.
As mentioned above, each switch's LSR specifies how the switch
connects to its neighbors. The connectivity information in an LSR
includes the switch's "domain identifier," and for each neighboring
(i.e., remote) switch, the remote switch's domain identifier,
remote port number and local port number. For example, as shown,
port 1 of switch 20 connects to port 7 of switch 22. For purposes
of this disclosure, the domain identifiers of each switch will be
the reference numerals shown in the various figures. Thus, "20" is
the domain identifier for switch 20, "22" is the domain identifier
for switch 22, and so on. The connectivity information contained in
the LSR 21 associated with switch 20 that describes the ISL between
ports 1 and 7 of switches 20 and 22 will include remote domain
identifier "22," local port number "1," and remote port number "7."
This type of information is included in LSR 21 for each ISL between
connecting switch 20 to a neighbor switch.
FIG. 2 shows an LSR 21 for switch 20. Each entry in the LSR
pertains to a separate ISL and other information (e.g., age,
incarnation number, etc.) may be included on the LSR. Because there
are four ISLs to switch 22, four ISLs to switch 26 and one ISL to
switch 28, the LSR 21 shown in FIG. 2 includes four entries
pertaining to neighboring switch 22, four entries pertaining to
neighboring switch 26 and one entry pertaining to neighboring
switch 28. Each entry identifies the local and remote ports forming
that ISL.
The last column in the LSR of FIG. 2 is labeled as "cost." Each ISL
in the network is assigned a cost value that is arbitrary in
magnitude, but inversely related to the bandwidth of the ISL. For
example, a 1 gigabit per second ("gbps") link may be assigned a
cost value of 1000, while a 2 gpbs link may be assigned a cost
value one-half as much (i.e., 500). As such, lower costs indicate
faster links The switches in the network preferably determine a
priori the lowest cost path between end points on the network by
adding together the costs of the various links forming each
possible path through the fabric and determining which path or
paths has the lowest total cost. The lowest cost path is selected
to be the path through which traffic is routed between end points.
For example, there are three possible paths for traffic to take
from device D1 to device D3 in FIG. 1. The three paths include
switches 20-22-24, 20-26-24, and 20-28-26-24. Whichever path has
the lowest total cost is the path assigned for traffic to be routed
from device D1 to device D3. In FIG. 2, the cost values are all set
at 1000, but in general the cost values can be different between
the various entries in the LSR and be changed as desired.
For data frames to be routed accurately and efficiently through the
fabric, each switch must be aware of the network's topology, that
is, how all of the switches are connected together. Each switch
initially only knows its connectivity information in its own LSR,
and not the LSR information pertaining to the other switches in the
fabric. Through a standardized synchronization process (described
below), the switches exchange LSR information and propagate such
information to other switches in the fabric. The collection of LSRs
associated with two or more switches is referred to herein as the
"topology database." The switches exchange their topology databases
so that each switch can be made aware of how other switches in the
network are connected together.
FIG. 3 depicts the standardized process for synchronizing the
topology databases of the switches in the fabric. The process
begins in step 30 when an ISL forms between a pair of switches.
Each switch detects when a physical connection is made to a
neighboring switch. In step 32, once a local switch detects one of
its ports is connected to a neighboring switch, the local switch
begins a "HELLO" protocol in which the switch sends HELLO messages
to the neighboring switch. The HELLO message essentially announces
the local switch's presence to the neighboring switch and includes
connectivity information for use by the neighboring switch. Such
connectivity information includes the local switch's domain, the
local switch's port number used for the new ISL and, if known, the
remote (i.e., neighboring) switch's domain and port number. These
values are included in various fields in the HELLO message. At
first, the local switch will not know the remote switch's domain
and port number and thus fills those fields in with predetermined
values such as all "F" hexadecimal values. The remote switch, once
it detects the new connection also begins sending HELLO messages
including the its domain and port numbers, leaving the other
switch's domain and port numbers as all F's. Thus, as indicated in
step 34, both switches provide each other their domain and port
number.
Once the switches are informed of the neighbor's domain and port
number, in step 36 the switches exchange their topology databases
which includes the LSRs describing all of the ISLs each switch
knows about. These databases may require more than one message
frame to complete the transfer. Thus, in step 38 once a switch has
sent all of its topology database to its new neighbor, the switch
sends a final frame that is precoded to indicate to the neighbor
that the neighbor has received all of the topology database. The
neighbor generally will not proceed to the next state in its state
machine until it receives this precoded end of database exchange
sequence frame. Once the end of the database exchange sequence
frame is received, the neighbor responds back with an
acknowledgment frame indicating that it has received the entire
topology database. In step 40 each switch then transitions the
state of the new ISL to the FULL state to permit the ISL to be used
for normal network traffic. Finally, each switch updates its own
LSR to include the connectivity information regarding the newly
established ISL and propagates the updated LSR via all other of its
ports to all other neighboring switches.
Each port on a switch performs the process outlined above when
physical connection from that port to a neighboring switch is
detected. Because the state machine for each port is the same, the
design of the switch is relatively straightforward. However, the
database synchronization process described above is inherently
inefficient because the same topology database is copied over each
and every link between the same pair of switches. The database
synchronization process works well when each switch has relatively
few ports, but the inherent inefficiency becomes more troublesome
as network switch technology progresses and the number of ports on
each switch increases. Today's switches typically have 16 ports and
64 port switches are becoming available. Thus, although the current
topology database synchronization process generally works well,
like most technology, improvements are always welcome. Moreover, an
improved topology database synchronization process is needed which
avoids or mitigates the inefficiency described above.
When there is a change in the state of an ISL (addition of
removal), the change is reflected in the LSR of the switches
(addition or removal of an entry) that detects the change. For each
change in the LSR of a switch, the switch needs to update its LSR
and transmit the new LSR on all other ISLs. This is also
inefficient and becomes troublesome as networks become larger and
the port count on the switches increase. Today's switches typically
have 16 ports and 64 port switches are becoming available. Thus,
although the current LSR update process generally works well, like
most technology, improvements are always welcome. Moreover, an
improved LSR update process is needed which avoids or mitigates the
inefficiencies described above.
BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The preferred embodiments of the present invention solve the
problems noted above by providing a network comprising a plurality
of interconnected switches that implements an improved topology
database synchronization technique. The technique involves each
switch detecting a newly formed physical connection to a
neighboring switch and only transmitting the switch's topology
database to the neighboring switch if the database has not already
been provided to the neighboring switch. When a new physical
connection is detected over one of the local switch's ports to a
neighboring switch, the local switch determines whether any of its
other ports have already been connected to the same neighboring
switch. If no other port on the local switch has been connected to
the neighboring switch, the local switch transmits its topology
database to the neighboring switch. If the local switch determines
that, in fact, it has already been connected to the neighboring
switch via another one of its ports, it is assumed that the local
switch's topology database has already been provided to the
neighboring switch. As such, the local switch does not copy yet
again the database to the neighboring switch.
The determination as to whether another port has already been
connected to the neighboring switch can be made by examining the
state of the ports on the local switch. For example, the local
switch examines its ports for a port that is in a state permitting
normal network traffic to be routed through the local switch to the
neighboring switch. A port in such as state indicates that the
switch's topology database has already been provided to the
neighboring switch. To provide backward compatibility with
conventional switches which, upon detecting a newly formed link,
await a topology database exchange, each switch in the preferred
embodiment transmits a frame indicating the end of a database
exchange frame despite not actually having transmitted the topology
database.
In conventional networks, once a switch has updated a link state
record to reflect a newly established inter-switch link, the
updated link state record is transmitted on all inter-switch links
to all other neighboring switches. In accordance with the preferred
embodiment of the invention, however, once a switch has updated a
link state record, the switch transmits the updated link state to
each neighboring switch via only one inter-switch link. With regard
to each neighboring switch, the local switch preferably chooses one
of its ports to be a "master" port for transmission of the updated
link state record. If the selected master port ceases to be usable
for routing network traffic, the local switch selects another port
to be the master with respect to the affected neighbor. Among the
available remaining ports connected to the neighboring switch, the
replacement master may be selected as the port having the lowest,
or highest, port number.
The topology database synchronization process described herein is
more efficient and uses less network resources than previous
synchronization techniques. These and other aspects and benefits of
the preferred embodiments of the present invention will become
apparent upon analyzing the drawings, detailed description and
claims, which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of the preferred embodiments of the
invention, reference will now be made to the accompanying drawings
in which:
FIG. 1 shows a network comprising a plurality of inter-connected
switches;
FIG. 2 shows an exemplary embodiment of a link state record usable
in each switch;
FIG. 3 depicts a conventional topology database synchronization
process;
FIG. 4 depicts a topology database synchronization process in
accordance with the preferred embodiment of the invention; and
FIG. 5 shows a more detailed embodiment of the process depicted in
FIG. 4.
NOTATION AND NOMENCLATURE.
Certain terms are used throughout the following description and
claims to refer to particular system components. As one skilled in
the art will appreciate, computer and computer-related companies
may refer to a component and sub-components by different names.
This document does not intend to distinguish between components
that differ in name but not function. In the following discussion
and in the claims, the terms "including" and "comprising" are used
in an open-ended fashion, and thus should be interpreted to mean
"including, but not limited to . . . ". Also, the term "couple" or
"couples" is intended to mean either a direct or indirect
electrical connection. Thus, if a first device couples to a second
device, that connection may be through a direct electrical
connection, or through an indirect electrical connection via other
devices and connections.
The present disclosure uses the terms "local," "remote," and
"neighboring" to refer to switches in the network. These terms are
not intended to impart any particular limitations on the switches.
Instead, these terms are simply intended to provide antecedent
basis for discussing switches in the network to make the discussion
clearer when discussing a switch in relation to a neighboring
switch. As such, when discussing the operation of switch, that
switch is referred to as the "local" switch and switches connected
to the local switch are referred to as "neighboring" or "remote"
switches. The terms "neighboring" and "remote" thus are used
synonymously in this disclosure.
To the extent that any term is not specially defined in this
specification, the intent is that the term is to be given its plain
and ordinary meaning.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following discussion is presented in the context of network
switches. It should be understood, however, that the principles
disclosed herein also apply to routers, switches and other types of
network devices.
Referring now to FIG. 4, in accordance with the preferred
embodiment of the invention, an improved network topology process
is shown as steps 50-56. Much of the functionality described below
is performed by each switch's CPU. The improved process is
particularly beneficial when multiple ISLs are formed between a
pair of neighboring switches. In step 50, the first ISL formed
between the pair of switches performs the HELLO, or equivalent,
protocol and the switch's topology databases are exchanged,
generally as described above. In step 52, for all subsequent ISLs
formed between the same pair of switches, the switches perform the
HELLO protocol to determine the domain and port number used by the
neighbor for the newly formed ISL. However, because the switches'
topology databases have already been exchanged (step 50), the
database exchange action preferably is bypassed. In this way, the
new ISLs are able to be brought up to the FULL state (step 54) much
faster and the synchronization process requires less operational
involvement from the switch and less network resources. Each switch
then updates its own LSR as shown in step 56.
A more detailed implementation of the process of FIG. 4 is shown in
FIG. 5. Other implementations are possible as well and should be
considered within the scope of this disclosure. Referring to FIG.
5, a switch detects a new physical connection over one of its ports
to a neighboring switch (step 60). The switch then begins the HELLO
protocol in step 62. Once the neighboring switch also begins its
HELLO protocol and the switches have successfully exchanged their
connectivity information regarding the newly formed ISL (step 64),
each switch determines in step 66 whether another ISL has already
been formed between the same pair of switches. This determination
can be made, for example, by determining the state of other ports
on the local switch. The local switch preferably examines its ports
to determine if a port exists that is in a state which permits
normal network traffic to be routed. An exemplary state in Fibre
Channel networks that is indicative of this condition is the FULL
state. The state of each port is maintained in memory (not
specifically shown) in each switch and is easily accessed to make
the determination of step 66. It is assumed that, if another port
is connected to the neighboring switch and is in a state that
permits the routing of network traffic, then the switch's topology
database has already been provided to the neighboring switch and
thus need not be copied again.
If no other port on the local switch is connected to the
neighboring switch and in the FULL state, then it is assumed that
the switch's topology database has not been transferred to the
neighboring switch. Accordingly, steps 68-74 are performed to
exchange the topology database (68), exchange frames indicating the
end of the topology database exchange (70), transition the new ISL
to the FULL state (72), and update the switch's LSR with
connectivity information from the newly formed ISL.
If, however, it is determined in step 66 that another ISL has
already been formed between the same pair of switches and such ISL
is in the FULL state, then it is assumed that the switch's topology
database has already been transferred to the neighboring switch.
Accordingly, the database exchange steps 68 and 70 preferably are
bypassed to avoid unnecessarily re-copying the database. At this
point, control can continue at step 72 in which the new ISL is
transitioned to the FULL state followed by updating the LSR (step
74).
In order to maintain "backward compatibility" with switches that do
not implement the improved topology database synchronization,
control may bypass step 68 but continue with step 70 as indicated
by the dashed line in FIG. 5. In step 70, the switch, having
determined that transferring a copy of its topology database to the
remote switch is unnecessary, transmits a frame to the neighboring
switch that indicates the end of the topology database exchange. By
transmitting the end of database exchange frame, even though the
database itself is not transferred, the remote switch, which may be
waiting for the end of the database exchange frame, is permitted to
continue with its operation.
In conventional fabric switches, once a switch's LSR is updated
(e.g., step 42 in FIG. 3), the new LSR is propagated to other
neighboring switches over all other ISLs. For example, with regard
to FIG. 1 after switch 20 adds an LSR to reflect a new ISL between
switches 20 and 22, the new LSR is transmitted to switch 26 via
port 9 and switch 28 via ports 5, 7, 8 and 2. As such, the same LSR
information may be transmitted multiple times to the same
neighboring switch if multiple ISLs exist to such neighboring
switch. This inefficiency results from (1) needing to transmit the
new LSR to each neighboring switch, and (2) implementing each
output port on a switch with the same state machine. That is, if
one port is designed to propagate a new LSR, all ports are designed
to propagate the LSR.
In accordance with the preferred embodiment of the invention, once
a switch's LSR is updated to include the description of a new ISL
(e.g., step 74 in FIG. 5), that new LSR is propagated to each
neighboring switch preferably over only one ISL connected to the
neighboring switch. With respect to FIG. 1, this means that switch
20 will transmit the updated LSR to switch 26 via only one output
port 5, 7, 8 or 2. This intelligent LSR propagation technique is
more efficient and consumes less system bandwidth than for
conventional implementations.
Propagating the LSR entry over only one of multiple ISLs between
neighboring switches requires one of the ports to be selected for
this function. In accordance with one embodiment of the invention,
the first ISL that is established (i.e., in the FULL state) from a
switch's output port to a neighboring switch is considered by the
switch to be the "master." All subsequently established ISLs to the
same neighbor are considered to be "slaves." Thus, when the switch
needs to transmit a new LSR entry to the neighbor, the LSR is
transmitted over only the master ISL. If the master ISL becomes
unusable for network communications for some reason, a new master
is selected. Among the remaining ISLs to the neighbor, the lowest
numbered port of the local switch preferably is selected as the new
master. For example, with respect to switch 26, if port 7 currently
is the master and the ISL between port 7 of switch 20 and port 2 of
switch 26 becomes unusable, then port 2 of switch 20 becomes the
new master for the purpose of propagating LSR updates. Of course,
if only one port/ISL exists when a master ISL becomes unusable,
then of course that one remaining port is used to transmit LSR
updates. Other techniques for selecting a replacement master are
possible as well. For example, selecting the highest numbered port,
rather than the lowest numbered port, is an acceptable technique.
Also, the master itself can be selected through alternate
techniques like using the lowest port number to be the master
(instead of using the first port that is usable for network
traffic).
As discussed above, an improved topology database synchronization
technique is provided which reduces the inefficiencies associated
with conventional database synchronization techniques. Broadly, as
little topology database information as possible is transmitted
between switches. This feature is more complex to implement than
conventional synchronization techniques, which blindly propagate
the database information on each and every ISL, but results in a
more efficient system that places less of a burden on network
resources such as bandwidth.
The above discussion is meant to be illustrative of the principles
and various embodiments of the present invention. Numerous
variations and modifications will become apparent to those skilled
in the art once the above disclosure is fully appreciated. It
should be understood, for example, that, as explained above, the
functionality of the network device (e.g., switch, router, gateway)
can be implemented as software instructions stored on a storage
medium and executed by a processor in the network device. It is
intended that the following claims be interpreted to embrace all
such variations and modifications.
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